With drives having two parallel shafts operated via a drive roller chain and corresponding chain wheels, e.g. for driving two upper positioned camshafts of a piston-type internal combustion engine, the problem frequently arises that the two shafts must be positioned relatively far apart as a result of the outside diameter of the chain wheels, which results from the transferring torque or the operating conditions of the drive shaft chain. With a camshaft drive on a piston-type internal combustion engine, the camshaft position relative to the position of the cylinder valves therefore cannot always be selected optimally. The arrangement of a gearwheel drive between the two shafts is costly and the arrangement of a chain transfer drive does not lead to the desired close positioning, owing to the necessary gearwheel outside diameter.
It is an object of the invention to solve the aforementioned problems with the aid of a chain drive.
According to the invention, this and other objects are solved with a chain drive for driving two parallel shafts located close to each other, in particular two upper positioned camshafts on a piston-type internal combustion engine. The drive is provided with a drive chain that is guided on the shafts by means of a drive and via chain wheels. At least one chain wheel is arranged on each shaft, wherein the chain wheels are axially offset relative to each other and are arranged overlapping. The chain wheel of one shaft is respectively associated with the support wheel on the other shaft, which supports and guides an edge region of the section of chain not engaged in a chain wheel on this shaft.
As a result of the offset and overlapping arrangement of the chain wheels on the two shafts, a narrower shaft spacing than specified for the chain wheel diameter can be realized. The two shafts are jointly driven via a chain, wherein the edge region of the chain section that is respectively not guided over a chain wheel is guided over a support wheel. The frictional losses correspond to that of a normal chain drive. The support wheel in this case can have a circular outside circumference. However, it is advantageous if the outer circumference of the support wheel has a polygonal shape, which essentially corresponds to the contour of the close-fitting chain region. With an embodiment having a multi-line drive chain (roller chain or bushing chain), the chain side bars rest on the support wheel. For an embodiment with a toothed chain, the edge of the toothed chain rests on the support wheel, so that the contour of the support wheel correspondingly can be designed as toothed wheel.
If a double-line or a multi-line drive chain is used, the chain wheels can be offset relative along their respective shaft relative to one another by approximately the distance between the chain sections.
If a toothed chain is used, the chain wheels and the at least one support wheel in an overlapping region define a total width corresponding to the width of the drive chain. The chain wheels and support wheels on each shaft can have a width equal to the width of the chain wheels and the support wheels on the other shaft.
In order to reduce the noise development, it is advantageous if a preferably locally arranged slider acts upon the chain strand that connects the two chain wheels. The slider causes a preferably slight deflection, thus reducing chain strand vibrations and a xe2x80x9cbeatingxe2x80x9d of the chain links when these are taken up by the chain wheel. The resulting slight increases in the frictional losses are countered by a reduction in the noise development. The level of the frictional losses also depends on the degree of tensioning of the chain strand by the slider.
The invention is not limited to drive chains, in particular the use of roller chains or bushing chains or toothed chains. In addition to a xe2x80x9cdrive chainxe2x80x9d in the true sense of the word, the terms xe2x80x9cdrive chainxe2x80x9d and xe2x80x9cchain wheelxe2x80x9d also cover a toothed belt and correspondingly a toothed belt pulley. The term xe2x80x9cchain drivexe2x80x9d within the meaning of this invention therefore also includes a toothed belt drive.